It is well known that a mode of an electromagnetic ("EM") field may be described as the sum of two quadrature components whose time variations are given by sine and cosine functions, respectively. The amplitude of each quadrature component is a variable having a complementary and uncertainty relationship with the other. The variances in these components and the resulting variations in the EM field in a vacuum state have long been recognized to generate a "shot noise" level providing a limit on the precision of measurements made with an EM field.
Quantum mechanisms has appreciated that the noise level can be reduced below the shot level by making the variances unequal; reduced fluctuations in one quadrature may be achieved by increasing the fluctuations in another quadrature (the so-called "squeezed states"). Such reductions would make possible significant advances in the precision of any EM field dependent measurement or process, such as spectroscopy, interferometry, communications and information storage.
Squeezed states have been generated by several optical processes that nonlineraly modify the amplification of the components in quadrature, including four-wave mixing and parametric oscillation, as described by B. G. Levy in Physics Today, pp. 17-19 (March 1986). However, the nonlinear optical interactions considered for squeezed state generation are often too weak to generate significant degrees of squeezing even over a single Reyleigh length. To remedy this situation optical cavities have been employed to enhance the effective nonlinearity with multiple passes through the intracavity medium. Variations in the intracavity medium adiabatically follow variations in the EM field within the cavity where such cavities are operated with the relaxation rate of the intracavity medium being very large compared decay rate of the EM field in the cavity.
We have found that significant degrees of squeezing may be achieved by appropriately coupling the EM field within the cavity to the nonlinear medium with modest values of atomic density and intracavity EM field. An oscillatory exchange of excitation between the atomic polarization and the EM field within the cavity then occurs. Such an exchange is precluded by those optical processes in which either the atomic or EM filed variables are adibatically eliminated.